Microwave
Regenerable GAC with Oxidation by Microwaves and Catalyst—(CHA Corp.)
Description of Technology
The CHA Corporation's technology removes solvents from gas streams by
adsorption onto GAC with regeneration of the saturated carbon by microwave energy. After desorption, the solvents or VOCs are
carried by a nitrogen purge gas stream to a destruction chamber where
microwaves induce oxidation reactions on the surface of a palladium catalyst. In addition to removing and destroying VOCs
from waste streams, the technology also removes sulfur dioxide (SO2)
and oxides of nitrogen (NOx). A zeolite bed can also be added to
remove ammonia and acid gases that are not easily adsorbed onto GAC. One system designed by the CHA Corporation
involves a transfer of the contaminated carbon to a separate regenerator for
desorption of the contaminants while another system has an “all-in-one”
adsorption and regeneration system.
Figure 1 below shows a diagram of the microwave air
purification system with all-in-one adsorption/regeneration and oxidation
system.
As the diagram
illustrates, the system has four main components, a moving-bed GAC/zeolite
adsorber, microwave regenerator, microwave oxidizer, and acid gas
adsorber. The moving-bed adsorber
continuously treats the air stream containing VOCs, hydrocarbons, solvents and
acid gases by adsorption of these contaminants onto the 4-inch thick moving bed
of 3-mm, 80 carbon tetrachloride number pelletized GAC, while the 2-inch thick,
4 X 8-mesh natural zeolite bed removes any acid gases and ammonia.
The
concentrated stream produced by the regeneration of the saturated GAC by
microwave energy, approximately 1% of the volume of the original air stream, is
then cooled and condensed to a liquid.
This liquid solvent is collected in a knockout pot (not shown), while
any remaining solvent vapor in the N2 sweep gas from the GAC
regenerator is fed into the microwave based catalytic oxidizer. The microwave catalyst reactor is packed
with an oxidizing
catalyst of platinum (Pt) and palladium (Pd) coated onto alumina beads
impregnated with 25 percent 800-mesh SiC.
The contaminant stream with solvents and gases in the N2 is
mixed with sufficient air for combustion and fed to the oxidizer. The microwaves and catalyst work together to
oxidize the concentrated solvent/acid gas-laden stream at low
temperatures. The
regenerated GAC and zeolite are then returned to the top of the adsorber. The combustion products from chlorinated
solvents will be CO2, H2O and HCl, which flows through an
acid gas scrubber. The scrubber is a
caustic impregnated carbon bed. Clean
air from the gas exiting the acid-gas removal bed is mixed with clean air from
the carbon/zeolite adsorber and vented to the atmosphere.
Figure 2 shows a picture
of the CHA vapor regeneration unit demonstrated at Edwards Air Force
Base. This unit is 1/10th
of the size of a full-scale system.
The CHA
technology allows the option of either recovering or destroying solvents,
ammonia, acids and other air pollutants and the continuous regeneration of the
GAC and zeolite on site. The company
claims that no secondary pollutants such as NOx are produced during
regeneration and the volume of gas production from the regeneration is 1% of
the volume of the contaminated air being treated. Therefore there is a 100 to 1 reduction in oxidation equipment
scale. The company also claims that the
microwave catalytic
oxidation of solvents, ammonia and acids eliminates any need for handling and
disposal of recovered wastes.
Additionally, less energy is required in the
regeneration process than in conventional GAC regeneration since the
temperatures are lower.
Vendor
CHA Corporation
372 West Lyon Street
Laramie, WY 82072